The present invention relates to the use of polyurethanes which are soluble or dispersible in water and are composed of
a) at least one compound which contains two or more active hydrogens per molecule,
b) at least one diol containing acid groups or salt groups and
c) at least one diisocyanate with a glass transition temperature of at least 15xc2x0 C. and acid numbers of from 12 to 150 or the salts of these polyurethanes as aids in cosmetic and pharmaceutical compositions, and to polyurethanes which are soluble or dispersible in water.
Polyurethanes which are at least partially biodegradable and contain hydroxy carboxylic acid copolymerized units have been disclosed. Either they are insoluble in water, like the polyurethane from polylactic acid diol and diisocyanate disclosed in SU-A-1 016 314, or they form films which are too soft, like the polyurethanes from poly(xcex5-caprolactone diol)dimethylolpropionic acid and diisocyanates disclosed in U.S. Pat. No. 4,098,743 and U.S. Pat. No. 4,147,679.
Water-soluble polyurethanes which contain carboxyl-containing diols as copolymerized units are disclosed in U.S. Pat. No. 3,412,054 and U.S. Pat. No. 3,658,939. They are used as adhesives and in coatings and printing inks. Sulfonate- and/or carboxylate-containing polyurethanes which are dispersible in water are disclosed in DE-A-15 70 615. They are used, for example, for coating and impregnating textiles, leather, paper, wood and metals.
In cosmetics, hair-treatment compositions which are, for example, in the form of setting preparations or sprays are used for setting, improving the structure and shaping the hair. These compositions are composed mainly of a solution of film-forming resins or synthetic polymers. The following film formers have hitherto been mainly used in such compositions: shellac, homo- and copolymers of N-vinylpyrrolidone, copolymers of vinyl ethers and maleic monoesters, of (meth)acrylic acid or the esters and amides thereof and crotonic acid with vinyl esters.
The hair-treatment compositions are applied to the hair by spraying in the form of solutions, preferably in ethanol. After the solvent has evaporated, the hair is held in in the desired shape by the polymer remaining at the points of contact. The polymers must, on the one hand, be sufficiently hydrophilic to be washed out of the hair but, on the other hand, be hydrophobic so that hair treated with the polymers retains its shape and does not become sticky even when the humidity is high.
The polymeric film formers disclosed to date, such as polyvinylpyrrolidones, usually have the disadvantage of excessive uptake of water when the humidity is high. This property results, inter alia, in unwanted adhesion of the hair and in a loss of strength of the setting, and thus collapse of the hair style. If, on the other hand, the resistance to high humidity is improved, eg. with copolymers of N-vinylpyrrolidone and vinyl acetate, the elasticity of the film suffers, and the brittleness of these films after the treatment of the hair may even result in unpleasant dust formation and a flaky coating. In addition, there are great difficulties in particular with washing out of the hair. The above-mentioned synthetic hair-treatment compositions are not biodegradable because their Cxe2x80x94C chain resists hydrolysis. Shellac is, on the other hand, biodegradable but has many disadvantages for the treatment of hair. Thus, its properties are not as good as those of the homo- and copolymers of N-vinylpyrrolidone, especially with regard to the adhesiveness, solubility in water and rigidity. Since shellac is a natural product, its properties are subject to wide variation.
It is an object of the present invention to provide aids for cosmetic and pharmaceutical compositions, as well as novel substances.
We have found that the first object is achieved by using polyurethanes which are soluble or dispersible in water and are composed of
a) at least one compound which contains two or more active hydrogens per molecule,
b) at least one diol containing acid groups or salt groups and
c) at least one diisocyanate with a glass transition temperature of at least 15xc2x0 C. and acid numbers of from 12 to 150 or the salts of these polyurethanes as aids in cosmetic and pharmaceutical compositions.
We have found that the other object is achieved by polyurethanes which are soluble or dispersible in water and are composed of
a) at least one compound which contains two or more active hydrogens per molecule,
b) at least one diol containing acid groups or salt groups and
c) at least one diisocyanate with acid numbers of from 12 to 150 or the salts of this polyurethane, which contain as compounds in group (a) at least 5 mol % of a polycondensate of lactic acid and of a polyol of the formula 
where
Y is a radical derived from a dihydric to tetrahydric alcohol,
n is 1-50 and
m is 1-4,
as copolymerized units.
Suitable for the use according to the invention are all polyurethanes which are soluble or dispersible in water, contain the abovementioned components a) to c) as copolymerized units, and have a glass transition temperature of at least 15xc2x0 C. and acid numbers of from 12 to 150, as well as the salts of the polyurethanes. Suitable compounds in group a) are all compounds which can be employed for preparing polyurethanes and have 2 or more active hydrogens per molecule. Examples of suitable compounds in group a) are diols, diamines, polyesterols, polyetherols or mixtures of said compounds, it being possible to replace up to 3 mol % of said compounds by triols or triamines. Examples of suitable diols are ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, polyetherols such as polyethylene glycols with molecular weights up to 3000, block copolymers of ethylene oxide and propylene oxide with number average molecular weights of up to 3000 or copolymers of ethylene oxide, propylene oxide and butylene oxide, which contain the alkylene oxide units distributed randomly or in the form of blocks. The diols and polyetherols preferably used are ethylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol and hexaethylene glycol.
Examples of suitable diamines are ethylenediamine, propylenediamine, 1,4-diaminobutane and hexamethylenediamine, as well as xcex1,xcfx89-diamines which can be prepared by the amination of polyalkylene oxides, especially polyethylene oxides, with ammonia.
Also suitable as compounds in group a) are all polyesterols which are normally employed to prepare polyurethanes, eg. products of the reaction of phthalic acid and diethylene glycol, isophthalic acid and 1,4-butanediol, isophthalic acid/adipic acid and 1,6-hexanediol, and adipic acid and ethylene glycol.
Particularly suitable polyesterols are poly(xcex1-hydroxy carboxylic acid diols) of the formula 
where
R1 and R2 are each H, C1-C5-alkyl or aryl,
R is a radical derived from a diol (alkylene radical) with 2-8 carbons,
n and m are each 1-30.
R in formula I is preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94, 
and R1 and R2 are preferably each CH3.
Examples of xcex1-hydroxy carboxylic acids which are suitable for preparing the poly(xcex1-hydroxy carboxylic acid diols) are lactic acid, xcex1-hydroxybutyric acid, lactide and glyoxylic acid. Lactic acid is preferably employed, and all the isomers are suitable: L-, D- and DL-lactic acid.
It is-also possible to use mixtures of compounds in group a) to prepare the polyurethanes, eg. mixtures of a diol and of a polyesterol, or of a diol and polyetherols. Up to 3 mol % of said compounds can be replaced by triols or triamines in the mixtures. Examples of suitable triols are glycerol, trimethylolethane or trimethylolpropane. Particularly suitable triamines are diethylenetriamine or dipropylenetriamine.
Compounds in group b) which can be employed to prepare the polyurethanes are all diols which contain acid groups or salt groups and are customary for this purpose. Particularly suitable are dimethylolpropanoic acid, compounds of the formula 
R in the formulae II and III is in each case a C2-C18-alkylene group and is preferably 
Me in formula III is Na or K.
The di- and polyisocyanates normally used can be used to prepare the polyurethanes. Particularly preferably used as compounds in group c) are hexamethylene diisocyanate, isophorone diisocyanate and/or toluylene diisocyanate. Chain extenders can be used as is customary in the preparation of polyurethanes. Examples of suitable chain extenders are hexamethylenediamine, piperazine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, neopentanediamine and 4,4xe2x80x2-diaminodicyclohexylmethane.
Biodegradable polyurethanes which are soluble or dispersible in water and contain as component a) at least 5 mol % of a polycondensate of lactic acid and of a polyol of the formula 
where
Y is a radical derived from a dihydric to tetrahydric alcohol,
n is 1-50 and
m is 1-4,
as copolymerized units are novel substances. Compounds of the formula IV can be obtained, for example, by esterifying a dihydric to tetrahydric alcohol with from 1 to 50 mol of lactic acid. Compounds in group a) which are preferably used are products of the reaction of diols with lactic acid, employing up to 50 mol, in particular from 5 to 30 mol, of lactic acid per mol of diol. Suitable examples of diols are ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol and 1,6-hexanediol, as well as polyetherols such as diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, copolymers of ethylene oxide and propylene oxide or copolymers of ethylene oxide, propylene oxide and butylene oxide, which may contain the alkylene oxide units in the form of blocks or in random distribution. The polyetherols have molecular weights up to 3000, preferably-up to 1000. The compounds of the formula IV can be used as component a) for preparing the novel polyurethanes either alone or mixed with other above-mentioned compounds of component a) which are normally employed to prepare polyurethanes. In mixtures of various compounds in group a) the compounds of the formula IV comprise at least 5, preferably at least 20, mol % of the mixture.
The above-mentioned novel polyurethanes can be obtained by reacting the compounds in groups a) and b) under an inert gas atmosphere in an inert solvent at from 70 to 130xc2x0 C. with the compounds in group c). This reaction can, where appropriate, be carried out in the presence of chain extenders in order to prepare polyurethanes of higher molecular weight. As is customary in the preparation of polyurethanes, the molar ratio of the components [(a)+(b)]:(c) is from 0.8 to 1.1:1. The acid number of the polyurethanes is determined by the composition and the concentration of the compounds of component (b) in the mixture of components (a)+(b). The polyurethanes have Fikentscher K values (determined in 0.1% by weight solutions in N-methylpyrrolidone at 25xc2x0 C. and pH 7) of from 15 to 100, preferably 25 to 50.
Substances which are likewise novel are biodegradable polyurethanes which are soluble or dispersible in water and which contain as component b) at least 5 mol % of a compound of the formula III 
where R is a C2-C18-alkylene group and Me is Na or K, as copolymerized units.
All the polyurethanes described above are used according to the invention as aids in cosmetic and pharmaceutical compositions. The polyurethanes employed in the cosmetic and pharmaceutical sector have acid numbers of-from 12 to 150, preferably 30 to 90, and a glass transition temperature of at least 15xc2x0 C. The glass transition temperature Tg can be up to 120xc2x0 C. and is preferably in the range from 30 to 100xc2x0 C. The glass transition temperature is determined by the ASTM D 3418 method.
The polyurethanes after neutralization (partial or complete) are soluble in water or dispersible in water without the assistance of emulsifiers. As a rule, the salts of the polyurethanes, which can be obtained therefrom by neutralization with bases, are more readily soluble or dispersible in water than are the non-neutralized polyurethanes. Bases which can be used for neutralizing the polyurethanes are alkali metal bases such as sodium or potassium hydroxide solution, sodium carbonate or bicarbonate, potassium carbonate or bicarbonate and alkaline earth metal bases such as calcium hydroxide, calcium oxide, magnesium hydroxide or magnesium carbonate, and ammonia and amines. Particularly suitable for neutralizing the polyurethanes containing acid groups for use in hair-treatment compositions are 2-amino-2-methyl-propanol, diethylaminopropylamine and triisopropanolamine. The polyurethanes containing acid groups can also be neutralized with the aid of mixtures of bases, eg. mixtures of sodium hydroxide solution and triisopropanolamine. The neutralization can vary depending on the intended use from partial, eg. 20-40%, to complete, ie. 100%.
If the compounds according to the invention are dispersible in water they can be used in the form of aqueous microdispersions with particle diameters of, normally, 5-100 nm, in particular 10-80 nm, and solids contents of, normally, 1-40% by weight, in particular 3-30% by weight. These microdispersions do not as a rule require emulsifiers or surfactants to stabilize them.
The polyurethanes derived from lactic acid polyols are at least partially biodegradable. All the polyurethanes containing acid groups are at least 90% eliminated in sewage sludge (determined by the Zahn-Wellens method in DIN 38 412, part 25).
The polyurethanes described above are used not only in hair cosmetics but also in creams and in the drugs sector as tablet coating compositions and tablet binders. The novel substances described above, which contain as characteristic constituents at least one compound of the formula IV as copolymerized units, can furthermore be used as sizes and as adhesives which are soluble in water. Particularly suitable polyurethanes for use as adhesive are those which contain copolymerized units of the formula IV and have glass transition temperatures below 15xc2x0 C. When the polyurethanes described above are used for hair treatment, they are usually employed in the form of aqueous or ethanolic solutions. The solids content of these solutions is from 0.1 to 30, preferably 1 to 15, % by weight of polyurethane or salt of a polyurethane.